The present invention is directed to apparatus for testing electronic devices having a high density array of pin leads such as a monolithic large scale integrated circuit.
Such circuits as above may have as many as one hundred pin leads. It is relatively difficult to provide a suitable test socket for such a pin array. For example, copending patent application Ser. No. 573,625 filed May 1, 1975, now U.S. Pat. No. 4,012,099 in the name of John L. Worcester, one of the co-inventors of the present application, and assigned to the present assignee and entitled "Zero Insertion Force Socket and Method Therefor" discloses and claims an improved socket for testing high density pin lead electronic devices.
However, it is desirable to provide a universal testing system for both hybrid and full scale integrated circuits and also to provide for both ac and dc tests. The ac tests include tests of propagation time and on hybrid circuit chips a voltage test. In general, in ac pulse testing it may be desirable that the pin is either terminated or unterminated in the characteristic impedance depending on the type of test desired. The testing device as a whole may be looked at a transmission line. In a hybrid chip in order to produce a full input voltage at the pin the line cannot be terminated at this point. However, on the other hand, for a time measurement there can be no reflection back to the input since this will otherwise make the measurement ambiguous. Thus, here the pin must be terminated.
In using a discriminator where measurement of the propagation time is being accomplished it is also desirable to prevent the loading down of the device under test by the discriminator. At the same time a proper termination is desirable to prevent secondary reflection.
Moreover, it is desirable to provide for universal dc testing by, for example, a Kelvin measurement technique which will compensate for lead resistance.
With a high density array of pins, capacitance problems are, of course, magnified. Also, it is difficult to gain access to the pins to test in a normal manner; for example, in a dc Kelvin test normally two separate leads are used to the pin itself in order to automatically cancel the effects of lead resistance in accordance with classical Kelvin bridge techniques.